Lonavala, as you must be knowing is in Mumbai, while Pavana Lake is outside Mumbai.
It approximately takes 1 hour to get to the lake from Lonavala. There are many direct and indirect ways to reach there.
The approximate distance between the two destinations are 33. 3 kms.
You can get to Pavana Lake from Lonavala via Pune too. It will take you a bus/train ride from Lonavala to Pune and then a car ride from Pune to Pavana Lake.
Via Panchgani, also it’s a bus and a car ride.
You can also get the lake through Satara and Mahabaleshwar.